A region-growing algorithm for InSAR phase unwrapping

Abstract

This paper describes a new region-growing algorithm for interferometric synthetic aperture radar (SAR) phase unwrapping. The algorithm is designed to handle noisy interferograms and is based on the following principles: 1) Unwrapping is carried out on the perimeter of "growth regions", and these regions are allowed to grow with consistency checking. 2) Phase information from neighboring pixels is used to predict the correct phase of each new pixel to be unwrapped. 3) Reliability check is applied to each unwrapping attempt, and the threshold used in the check is gradually relaxed so that the most robust unwrapping path is followed. 4) As regions grow into one another, they are merged by adjusting their ambiguity numbers, and further reliability checks must be passed for merging to be allowed. To verify the proposed algorithm, the region-growing phase unwrapping algorithm has been compared with two of the most widely used algorithms: the cut-line (CL) (also known as residue-linking) algorithm and the weighted least-squares (WLS) algorithm. The FRINGE Sardegna interferogram has been used because it has steep topography that causes problems for many phase unwrapping algorithms. It has been shown that the region-growing algorithm can unwrap well into low coherence regions, while making few ambiguity-level errors. This can be attributed to the diversity of growth paths used by the algorithm, in which difficult areas are approached from many directions.